An Advanced Catalytic Solvent for Lower Cost Post-Combustion CO 2 Capture in a Coal-Fired Power Plant
In this report, CAER addresses DOE’s objectives for improvements on post-combustion CO 2 capture through a three-fold approach including 1) advanced solvent, 2) homogeneous catalyst and 3) membrane carbon enrichment system. CAER-B3 solvent was formulated to improve the overall thermodynamics with the addition of a proton receiver while maintaining faster kinetics with the addition of thermally robust primary amine. The EH&S study indicates that CAER-B3 solvent poses little human toxicological or ecological risk in its raw material form. Generation of significant quantities of nitrosamines was deemed unlikely when using B3 solvent for CO 2 capture from coal-derived flue gas. The catalytic solvent caused a 21% reduction in energy demand, achievable via decreasing the liquid flowrate. Cyclic capacity nearly doubled due to the slower flowrate, and therefore, reduced the sensible heat required to remove CO 2 in the stripper. The increased rich loadings achieved by either pre-concentrating membrane or dewatering membrane prior to stripper, in addition to improved cyclic capacity, will lower downstream compression costs, while reducing the energy consumption per unit of CO 2 produced. Moreover, the CAER-B3 solvent demonstrated a greater thermal stability, lessening the rate of amine loss, caused by solvent degradation and emissions, by 50-70%. The CAER developed catalysts with a second order rate constant of 7.5 x 10 4 – 10 5 M -1 s -1 , far beyond those reported to date. The catalyst was designed to be a mimic of the enzyme carbonic anhydrase and increase the rate of CO 2 hydration to produce bicarbonate. As such, a 10-25% improvement in absorption rate was observed over the MEA base case. Enhancements can be imparted to the full scale system to reduce packing height of the absorber column, resulting in significant capital cost savings. Furthermore, the family of CAER catalysts showed less than 10% decomposition over 100 hours at 100 °C, suggesting that these catalysts will be stable in the harsh oxidative and thermal process conditions of an industrial carbon capture unit. Flue gas contaminants, such as NO x and SO x , also did not impact catalytic activity. A method for synthetic production of 500 g/batch was designed, verified, and well-documented, with scaling capabilities up to 500 kg. Two types of membranes were designed and tested for the purpose of increasing the solvent carbon loading prior to entering the stripper column. 500 hour and 100 hour verification studies were completed for the pre-concentrating membrane and zeolite dewatering membrane, respectively. Results demonstrated that a membrane-based CO 2 enrichment step using a commercial CO 2 membrane, or a zeolite dewatering membrane, or both, should be implemented in the carbon capture process to increase the CO 2 partial pressure by 16%, resulting in a stripping energy reduction of 35% relative to DOE Case 12 MEA solvent. Experimental data showed a carbon loading enrichment of 18-40% in comparison to the configuration without the pre-concentrating gas membrane. During the timespan of this project, challenges were identified and addressed so that enhanced performance may be realized long-term. Mitigation implementations included re-configuration of the bench unit with a solvent recovery column and a knock-out drum, as well as an increase in stripper pressure set point. Both changes resulted in a considerable reduction in the rate of solvent loss. Additionally, the membrane synthesis procedure was modified and validated to address zeolite dissolution concerns along with a new separation module. The techno-economic analysis conducted by WorleyParsons indicated the CAER-adCCS hybrid approach may outperform NETL Case 12 with regards to net plant HHV efficiency and cost of electricity.